The present invention relates to the navigation of an aircraft and in particular to a means for determining the position of an aircraft with respect to a runway.
Upon aircraft landing, adverse weather conditions such as heavy fog or rain, causing low visibility, can result in particularly hazardous conditions. Therefore, despite a sophisticated digital avionic system installed on the present generation of aircrafts which defines aircraft's altitude, speed, and distance from a runway with great precision, there are defined minimum weather conditions required before an aircraft can continue an approach to a landing. These weather conditions take into account the capabilities of the aircraft and the pilot, and the equipment installed at the airport and require minimum ceiling and minimum runway visibility because of possibility for an incident to occur. While making an instrumental approach, an incident may occur because of even small error, either of equipment installed at an airport or of an onboard avionic system. A missed approach, which results either in a go-around procedure and another attempt to land or a flight to an alternate airport, causes huge expenses to airline company and great inconvenience for passengers.
The well-known Instrument Landing System (ILS) and Microwave Landing System (MLS), together with other related means such as Distance Measuring Equipment (DME), provide the pilot and/or digital avionic system with accurate information for an approach and landing. These instruments provide a technique for reaching an end-of-descent point with great precision. Ideally, once cleared for descent, an aircraft is left alone to perform the descent from a top-of-descent point along descent path to an end-of-descent point where a final flare-out occurs.
A flare-out or flare, which is that portion of the landing trajectory between the fixed angle glide slope and the touchdown point on a runway, is the critical portion of the aircraft landing trajectory during which a pilot must decide either to continue the landing procedure or to abort the landing and effect the go-around. Since the systems disclosed in the prior art may not provide the pilot with a completely accurate position of the aircraft with respect to the runway longitudinal axis and plane due to the susceptibilities of the systems, visual contact is necessary to perform a completely safe landing. The visual contact with the runway must be possible before the point where the pilot can still effect a completely safe go-around procedure and, therefore, conditions where low visibility occurs, mostly due to heavy fog, prevent landing on airports sometimes for substantial periods of time.
Therefore, it is an object of the present invention to provide an inexpensive system which will enable the pilot to determine the position of the aircraft with respect to the runway with greater precision than when using only systems know in the prior art. It is an assumption that the present invention does not eliminate presently used systems and acts accordingly with any of them by supplying the digital avionic system with more accurate additional information regarding the aircraft position with respect to the runway.
The present invention enables the pilot to position the aircraft exactly towards the runway longitudinal axis and plane and effect a safe landing, even in almost zero-zero visibility conditions. Acting accordingly with existing systems, the present invention can be used as a reliable and independent secondary means of detecting an accidental error which may occur due to susceptibility of ILS' or MLS' means.